A method for manufacturing a layered product having alternating resin layers and metal thin film layers, wherein depositing a resin layer and depositing a metal thin film layer are performed one after the other, and repeatedly applied to a rotating supporting base, is known, for example, from European Patent Application EP 0 808 667.
Referring to the drawings, the following is an example of a method for manufacturing a layered product comprising resin layers and metal thin film layers.
FIG. 12 is a cross-sectional drawing schematically showing an example of a manufacturing apparatus using a conventional method for manufacturing a layered product.
An apparatus 900 for manufacturing a layered product comprises a rotatable cylindrical can roller 910 inside a vacuum tank 901, an apparatus 920 for forming a resin layer arranged near the perimeter of the can roller 910, a resin curing device 940, and an apparatus 930 for forming a metal thin film. The reduced pressure inside the vacuum tank 901 is sustained by a vacuum pump 902.
Liquid resin material is supplied to the apparatus 920 for forming a resin layer with a resin-material supply tube 921. The fluid flow can be regulated with a fluid-flow regulation valve 922. The fluid resin material is accumulated in a heating container 923, heated, evaporated, and deposited on the surface of a heating roll 925, which rotates in the direction indicated by arrow 924. Then, it is again evaporated, and deposited on the surface of the can roller 910, which rotates in the direction indicated by arrow 911.
Since the can roller 910 has been cooled below the condensation point of the resin material, the deposited resin material is cooled by the surface of the can roller 910, so that a solid resin layer made of the resin material is formed.
The resulting resin layer is cured by irradiation of UV light from the resin curing device 940.
Then, the apparatus 930 for forming a metal thin film forms an aluminum thin film on the surface of the resin layer by vapor deposition.
Thus, rotating the can roller 910, the apparatus 920 for forming a resin layer and the apparatus 930 for forming a metal thin film form resin layers alternating with metal thin film layers on the circumferential surface of the can roller 910, and a layered product comprising resin layers and metal thin film layers is manufactured.
Considerable R&D efforts have been invested in this method, since with this method, a resin layer thickness of about 0.1-1 .mu.m, and a metal thin film layer thickness of about 50 nm can be attained. A compact capacitor with large capacitance can be manufactured with low production costs when the obtained layered product is applied to a capacitor with the resin layers as the dielectric layers.
However, when the above method is reduced to practice, a number of problems remain to be solved.
First, as the thicknesses of the resin layer and the metal thin film layer become very thin, the existence of solid foreign particles in the layered product cannot be ignored anymore. Small solid foreign particles adhering to the surface of the can roller 910 are particularly abundant in the layered product that is the first one manufactured after closing the vacuum tank 901, which had been opened for performing adjustments on the apparatuses inside it. FIG. 13 is a cross-sectional drawing, showing schematically the layering of resin layers 951 and metal thin film layers 952 when a solid foreign particle 961 adheres to the surface of the can roller 910. As is shown in this drawing, when the layer thickness is thin, the relative size of the foreign particle in comparison to the thickness of each layer cannot be ignored, and a protrusion 956 that is bigger than the intruding foreign particle is formed on the surface of the resulting layered product. Moreover, the thicknesses of the resin layer and the metal thin film layer at the portion where the protrusion is formed easily become irregular. Consequently, if the layered product is used, for example, as a capacitor, the withstand voltage of the capacitor decreases due to the presence of portions where the resin films are thinner, and in the worst case, pinholes develop and cause short-circuits. Moreover, when the metal thin film layer becomes too thin, the withstand current of that portion may decrease. It follows that there is a need for a method for manufacturing layered products with reduced chances for the presence of foreign particles.
There are applications for the layered product, where it is especially desirable for the layering thicknesses of the layered product to be precisely as designed. Furthermore, when the metal thin film layer is divided into a plurality of metal thin film layer portions formed on the same resin layer surface by forming insulating regions (also called "margins") where the metal thin film layer is not formed, it is desirable that the position of the insulating regions and their widths be precisely as designed. If the layered product is used as a capacitor for example, the thickness of the resin layers, which function as the dielectric layers, and the position and the widths of the insulating regions, which determine the surface area of the portions that function as the dielectric, have a direct influence on the capacitance of the capacitor. Heretofore, the manufacturing parameters were determined by theoretical calculations or by trial and error. However, since it is very difficult to maintain the manufacturing environment (atmosphere) constant, the resulting layered products are not necessarily identical, even when identical settings are used as manufacturing parameters. Furthermore, there is a limit to the precision with which the actual layering of a thin film can be predicted by theoretical calculations. Consequently, there is a need for a method, wherein, before the layered product is formed, a resin layer and a metal thin film layer, and if necessary insulating regions, are formed, it is checked how well they were formed, optimal manufacturing conditions are determined and set on the basis of this check, and the layered product is manufactured subsequently and without modifying environment (atmosphere) and the conditions after their optimization.